Methods for treating thermoplastic polyurethane covers for golf balls with epoxy compositions

ABSTRACT

Golf balls having covers made of thermoplastic polyurethane compositions are provided. Multi-piece golf balls can be made. In one embodiment, the outer cover layer is formed from a composition comprising a thermoplastic polyurethane and epoxy compound. Mixtures of multi-functional amines and imines, and multi-functional isocyanates, and epoxy curing agents; and solvent, can be applied to the outer cover. The resulting coating may contain polyurethanes, polyureas, and hybrids, copolymers, and blends thereof. The cover composition and surface coatings can further include catalysts, ultraviolet (UV)-light stabilizers, and other additives. The coating methods have many benefits and the finished balls have good physical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 16/001,011, filed on Jun. 6, 2018, which is a continuation-in-partof U.S. patent application Ser. No. 15/786,644, filed on Oct. 18, 2017,now U.S. Pat. No. 10,363,458, which is a continuation-in-part of U.S.patent application Ser. No. 15/710,866, filed on Sep. 21, 2017, now U.S.Pat. No. 10,252,113, the entire disclosures of which are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to golf balls having covers madeof thermoplastic polyurethane compositions. The golf ball includes aninner core and surrounding thermoplastic polyurethane outer cover.Multi-piece golf balls having outer cores, inner covers, andintermediate layers can be made. Blends of thermoplastic polyurethanesand epoxy compounds can be used to make the cover. The methods alsoinclude treating the balls with multi-functional amine, imine,isocyanate compounds and epoxy curing agents. The invention alsoencompasses the resulting balls. The finished balls with thermoplasticpolyurethane covers have many advantageous physical and playingperformance properties.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

Three-piece, four-piece, and even five-piece balls have become morepopular over the years. More golfers are playing with these multi-pieceballs for several reasons including new manufacturing technologies,lower material costs, and desirable ball playing performance properties.Many golf balls used today have multi-layered cores comprising an innercore and at least one surrounding outer core layer. For example, theinner core may be made of a relatively soft and resilient material,while the outer core may be made of a harder and more rigid material.The “dual-core” sub-assembly is encapsulated by a single ormulti-layered cover to provide a final ball assembly. Differentmaterials are used in these golf ball constructions to impart specificproperties and playing features to the ball.

For instance, in recent years, there has been high interest in usingpolyurethane compositions to make golf ball covers. Basically,polyurethane compositions contain urethane linkages formed by reactingan isocyanate group (—N═C═O) with a hydroxyl group (OH). Polyurethanesare produced by the reaction of a multi-functional isocyanate with apolyol in the presence of a catalyst and other additives. The chainlength of the polyurethane prepolymer is extended by reacting it withhydroxyl-terminated and amine curing agents.

In Sullivan et al., U.S. Pat. No. 5,971,870, thermoplastic orthermosetting polyurethanes and ionomers are described as being suitablematerials for making outer cover and any inner cover layer. The coverlayers can be formed over the cores by injection-molding, compressionmolding, casting or other conventional molding techniques. Preferably,each cover layer is separately formed. In one embodiment, the innercover layer is first injection molded over the core in a cavity mold,subsequently any intermediate cover layers are injection molded over theinner cover layer in a cavity mold, and finally the outer cover layer isinjection molded over the intermediate cover layers in a dimpled cavitymold.

In Sullivan et al., U.S. Pat. No. 7,131,915, the outer cover can be madefrom a polyurethane composition and various aliphatic and aromaticdiisocyanates are described as being suitable for making thepolyurethanes. Depending on the type of curing agent used, thepolyurethane composition may be thermoplastic or thermoset in nature.Sullivan '915 further discloses that compositions for the intermediatecover layer and inner cover layer may be selected from the same class ofmaterials as used for the outer cover layer. In other embodiments,ionomers such as HNPs, can be used to form the intermediate and innercover layers. The castable, reactive liquid used to form the urethaneelastomer material can be applied over the core using a variety oftechniques such as spraying, dipping, spin coating, or flow coatingmethods.

As discussed above, both thermoplastic and thermosetting polyurethanescan be used to form golf ball covers. Thermoplastic polyurethanes haveminimal cross-linking; any bonding in the polymer network is primarilythrough hydrogen bonding or other physical mechanism. Because of theirlower level of cross-linking, thermoplastic polyurethanes are relativelyflexible. The cross-linking bonds in thermoplastic polyurethanes can bereversibly broken by increasing temperature such as during molding orextrusion. That is, the theremoplastic material softens when exposed toheat and returns to its original condition when cooled. On the otherhand, thermoset polyurethanes become irreversibly set when they arecured. The cross-linking bonds are irreversibly set and are not brokenwhen exposed to heat. Thus, thermoset polyurethanes, which typicallyhave a high level of cross-linking, are relatively rigid.

One advantage with using thermoplastic polyurethane compositions to formgolf ball covers is that they have good processability. Thethermoplastic polyurethanes generally have good melt-flow properties anddifferent molding methods may be used to form the covers. Althoughthermoplastic polyurethane covers for golf balls have been used over theyears, there are drawbacks with using some thermoplastic polyurethanesmaterials. For example, one drawback with some thermoplasticpolyurethanes is they may not be as durable and tough as other polymers.For example, the resulting thermoplastic polyurethane cover may not havehigh mechanical strength, impact durability, and cut and scuff (grooveshear)-resistance.

Thus, manufacturers have used various methods of treating thermoplasticpolyurethanes to enhance the durability and strength of the polymer. Forexample, an isocyanate may be compounded into a masterbatch and then themasterbatch may be added to the thermoplastic polyurethane compositionprior to molding. In another example, the molded thermoplasticpolyurethane cover may be dipped into an isocyanate solution. Treatingthe thermoplastic polyurethane material with isocyanates helps improvethe physical properties such as mechanical strength, impact durability,and cut and scuff (groove shear)-resistance of the material. In somecases, the physical properties may not only increase, but they mayactually increase beyond the values of the non-refined material.

For example, Kennedy, III, U.S. Pat. No. 8,920,264 and Matroni, U.S.Pat. No. 9,119,990 disclose isocyanate dipping methods, whereby a golfball having a thermoplastic polyurethane cover is treated with asolution of isocyanate. The isocyanate solution can contain a solvent,for example, acetone or methyl ethyl ketone (MEK), at least oneisocyanate compound, and a catalyst. The ball is soaked in theisocyanate solution and this causes the isocyanate compound to permeatethe cover. The isocyanate compound cross-links the thermoplasticpolyurethane cover material, and this improves the physical propertiesof the cover such as durability and scuff-resistance.

One drawback with using conventional isocyanate treatment methods isthey typically require additional steps in the manufacturing process andthey may not be very cost-effective. These additional steps may betime-consuming and reduce process efficiency. In view of some of thedrawbacks with some of these methods, it would be desirable to have new,cost-effective, efficient methods that can produce golf balls withdesirable physical and playing performance properties. The presentinvention provides new methods for making thermoplastic polyurethanecovers for golf balls having many advantageous features and benefits.The invention also includes the resulting golf balls having goodphysical and playing performance properties.

SUMMARY OF THE INVENTION

The present invention generally relates to golf balls having covers madeof thermoplastic polyurethane compositions. The invention includes amethod for treating a golf ball cover, comprising the steps of: a)providing a golf ball sub-assembly comprising at least one core layer;b) forming an outer cover layer over the sub-assembly, wherein the outercover layer is formed from a first composition comprising athermoplastic polyurethane; and c) applying a second compositioncomprising an epoxy-functional compound to the outer cover layer.Suitable epoxy-functional compounds include, for example, glycidylmethacrylate, glycidyl acrylate, diglycidyl ether of bisphenol A,diglycidyl ether of bisphenol F, 1,4-cyclohexanedimethanol diglycidylether, 1,4-butanediol diglycidyl ether, trimethylolpropane triglycidylether; and mixtures thereof. The second composition can further containan epoxy curing agent such as, for example, amines, acids, anhydrides,imines, isocyanates, and hydroxyls, and mixtures thereof. Solvents suchas ketones, acetates, and mixtures thereof can be used to prepare thecompositions. Also, additives such as ultraviolet (UV) light stabilizerand catalysts can be included in the compositions.

In a second embodiment, the treatment method involves the steps of: a)providing a golf ball sub-assembly comprising at least one core layer;b) forming an outer cover layer over the sub-assembly, wherein the outercover layer is formed from a first composition comprising athermoplastic polyurethane and epoxy-functional compound; c) applying asecond composition comprising an epoxy curing agent to the outer coverlayer to form at least a partially cross-linked cover for the golf ball.

In another embodiment, the method includes the steps of: a) providing agolf ball sub-assembly comprising at least one core layer; b) forming anouter cover layer over the sub-assembly, wherein the outer cover layeris formed from a first composition comprising a thermoplasticpolyurethane and epoxy curing agent; and c) applying a secondcomposition comprising an epoxy-functional compound to the outer coverlayer to form at least a partially cross-linked cover for the golf ball.In yet another embodiment, the method includes the steps of: a)providing a golf ball sub-assembly comprising at least one core layer;b) forming an outer cover layer over the sub-assembly, wherein the outercover layer is formed from a first composition comprising athermoplastic polyurethane; c) applying a second composition comprisingan epoxy-functional compound to the outer cover layer; and d) applying athird composition comprising an epoxy curing agent to the outer coverlayer to form at least a partially cross-linked cover for the golf ball.The invention also includes golf balls having an outer cover produced bythe above-described methods and other treatment methods describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a dimpled golf ball made in accordancewith the present invention;

FIG. 2 is a cross-sectional view of a two-piece golf ball having aninner core and outer cover made in accordance with the presentinvention;

FIG. 3 is a cross-sectional view of another two-piece golf ball havingan inner core and outer cover made in accordance with the presentinvention;

FIG. 4 is a cross-sectional view of a three-piece golf ball having aninner core, outer core, and outer cover made in accordance with thepresent invention;

FIG. 5 is a partial cut-away perspective view of a three-piece golf ballhaving an inner core, outer core, and outer cover made in accordancewith the present invention; and

FIG. 6 is a cross-sectional view of a four-piece golf ball having aninner core, outer core, inner cover, and outer cover made in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to golf balls having covers madeof thermoplastic polyurethane (TPU) compositions. Different polyurethaneprimer and top-coats are applied to the polyurethane outer cover inaccordance with this invention. The invention also includes the finishedgolf balls made from these coating applications.

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a two-piece golf ballcontaining a core and having a surrounding cover is made. Three-piecegolf balls containing a dual-layered core and single-layered cover alsocan be made. The dual-core includes an inner core (center) andsurrounding outer core layer. In another version, a four-piece golf ballcontaining a dual-core and dual-cover (inner cover and outer coverlayers) is made. In yet another construction, a four-piece or five-piecegolf ball containing a dual-core; casing layer(s); and cover layer(s)may be made. As used herein, the term, “casing layer” means a layer ofthe ball disposed between the multi-layered core sub-assembly and cover.The casing layer also may be referred to as a mantle or intermediatelayer. The diameter and thickness of the different layers along withproperties such as hardness and compression may vary depending upon theconstruction and desired playing performance properties of the golf ballas discussed further below.

Core Structure

The golf ball may contain a single- or multi-layered core. In onepreferred embodiment, at least one of the core layers is formed of arubber composition comprising polybutadiene rubber material. Moreparticularly, in one version, the ball contains a single inner coreformed of the polybutadiene rubber composition. In a second version, theball contains a dual-core comprising an inner core (center) andsurrounding outer core layer.

In one version, the core is formed of a rubber composition comprising arubber material such as, for example, polybutadiene, ethylene-propylenerubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadienerubber, polyalkenamers, butyl rubber, halobutyl rubber, or polystyreneelastomers. For example, polybutadiene rubber compositions may be usedto form the inner core (center) and surrounding outer core layer in adual-layer construction. In another version, the core may be formed froman ionomer composition comprising an ethylene acid copolymer containingacid groups such that greater than 70% of the acid groups areneutralized. These highly neutralized polymers (HNPs) also may be usedto form at least one core layer in a multi-layered core construction.For example, a polybutadiene rubber composition may be used to form thecenter and a HNP composition may be used to form the outer core. Suchrubber and HNP compositions are discussed in further detail below.

In general, polybutadiene is a homopolymer of 1, 3-butadiene. The doublebonds in the 1, 3-butadiene monomer are attacked by catalysts to growthe polymer chain and form a polybutadiene polymer having a desiredmolecular weight. Any suitable catalyst may be used to synthesize thepolybutadiene rubber depending upon the desired properties. Normally, atransition metal complex (for example, neodymium, nickel, or cobalt) oran alkyl metal such as alkyllithium is used as a catalyst. Othercatalysts include, but are not limited to, aluminum, boron, lithium,titanium, and combinations thereof. The catalysts produce polybutadienerubbers having different chemical structures. In a cis-bondconfiguration, the main internal polymer chain of the polybutadieneappears on the same side of the carbon-carbon double bond contained inthe polybutadiene. In a trans-bond configuration, the main internalpolymer chain is on opposite sides of the internal carbon-carbon doublebond in the polybutadiene. The polybutadiene rubber can have variouscombinations of cis- and trans-bond structures. A preferredpolybutadiene rubber has a 1,4 cis-bond content of at least 40%,preferably greater than 80%, and more preferably greater than 90%. Ingeneral, polybutadiene rubbers having a high 1,4 cis-bond content havehigh tensile strength. The polybutadiene rubber may have a relativelyhigh or low Mooney viscosity.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29IVIES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; and DIENE 55NF, 70AC, and 320 AC, availablefrom Firestone Polymers of Akron, Ohio.

To form the core, the polybutadiene rubber is used in an amount of atleast about 5% by weight based on total weight of composition and isgenerally present in an amount of about 5% to about 100%, or an amountwithin a range having a lower limit of 5% or 10% or 20% or 30% or 40% or50% and an upper limit of 55% or 60% or 70% or 80% or 90% or 95% or100%. In general, the concentration of polybutadiene rubber is about 45to about 95 weight percent. Preferably, the rubber material used to formthe core layer comprises at least 50% by weight, and more preferably atleast 70% by weight, polybutadiene rubber.

The rubber compositions of this invention may be cured, either bypre-blending or post-blending, using conventional curing processes.Suitable curing processes include, for example, peroxide-curing,sulfur-curing, high-energy radiation, and combinations thereof.Preferably, the rubber composition contains a free-radical initiatorselected from organic peroxides, high energy radiation sources capableof generating free-radicals, and combinations thereof. In one preferredversion, the rubber composition is peroxide-cured. Suitable organicperoxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions preferably include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur or metal saltthereof, organic disulfide, or inorganic disulfide compounds may beadded to the rubber composition. These compounds also may function as“soft and fast agents.” As used herein, “soft and fast agent” means anycompound or a blend thereof that is capable of making a core: 1) softer(having a lower compression) at a constant “coefficient of restitution”(COR); and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber compositions of the present invention also may include“fillers,” which are added to adjust the density and/or specific gravityof the material. Suitable fillers include, but are not limited to,polymeric or mineral fillers, metal fillers, metal alloy fillers, metaloxide fillers and carbonaceous fillers. The fillers can be in anysuitable form including, but not limited to, flakes, fibers, whiskers,fibrils, plates, particles, and powders. Rubber regrind, which isground, recycled rubber material (for example, ground to about 30 meshparticle size) obtained from discarded rubber golf ball cores, also canbe used as a filler. The amount and type of fillers utilized aregoverned by the amount and weight of other ingredients in the golf ball,since a maximum golf ball weight of 45.93 g (1.62 ounces) has beenestablished by the United States Golf Association (USGA).

Suitable polymeric or mineral fillers that may be added to the rubbercomposition include, for example, precipitated hydrated silica, clay,talc, asbestos, glass fibers, aramid fibers, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,tungsten carbide, diatomaceous earth, polyvinyl chloride, carbonatessuch as calcium carbonate and magnesium carbonate. Suitable metalfillers include titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, lead, copper, boron, cobalt, beryllium, zinc, and tin.Suitable metal alloys include steel, brass, bronze, boron carbidewhiskers, and tungsten carbide whiskers. Suitable metal oxide fillersinclude zinc oxide, iron oxide, aluminum oxide, titanium oxide,magnesium oxide, and zirconium oxide. Suitable particulate carbonaceousfillers include graphite, carbon black, cotton flock, natural bitumen,cellulose flock, and leather fiber. Micro balloon fillers such as glassand ceramic, and fly ash fillers can also be used. In a particularaspect of this embodiment, the rubber composition includes filler(s)selected from carbon black, nanoclays (e.g., Cloisite® and Nanofil®nanoclays, commercially available from Southern Clay Products, Inc., andNanomax® and Nanomer® nanoclays, commercially available from Nanocor,Inc.), talc (e.g., Luzenac HAR® high aspect ratio talcs, commerciallyavailable from Luzenac America, Inc.), glass (e.g., glass flake, milledglass, and microglass), mica and mica-based pigments (e.g., Iriodin®pearl luster pigments, commercially available from The Merck Group), andcombinations thereof. In a particular embodiment, the rubber compositionis modified with organic fiber micropulp.

In addition, the rubber compositions may include antioxidants to preventthe breakdown of the elastomers. Also, processing aids such as highmolecular weight organic acids and salts thereof, may be added to thecomposition. In a particular embodiment, the total amount of additive(s)and filler(s) present in the rubber composition is 15 wt % or less, or12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt % orless, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, based onthe total weight of the rubber composition.

The polybutadiene rubber material (base rubber) may be blended withother elastomers in accordance with this invention. Other elastomersinclude, but are not limited to, polybutadiene, polyisoprene, ethylenepropylene rubber (“EPR”), styrene-butadiene rubber, styrenic blockcopolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and thelike, where “S” is styrene, “I” is isobutylene, and “B” is butadiene),polyalkenamers such as, for example, polyoctenamer, butyl rubber,halobutyl rubber, polystyrene elastomers, polyethylene elastomers,polyurethane elastomers, polyurea elastomers, metallocene-catalyzedelastomers and plastomers, copolymers of isobutylene and p-alkylstyrene,halogenated copolymers of isobutylene and p-alkylstyrene, copolymers ofbutadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber,chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber,and combinations of two or more thereof.

The polymers, free-radical initiators, filler, cross-linking agents, andany other materials used in forming either the golf ball center or anyportion of the core, in accordance with invention, may be combined toform a mixture by any type of mixing known to one of ordinary skill inthe art. Suitable types of mixing include single pass and multi-passmixing, and the like. The cross-linking agent, and any other optionaladditives used to modify the characteristics of the golf ball center oradditional layer(s), may similarly be combined by any type of mixing. Asingle-pass mixing process where ingredients are added sequentially ispreferred, as this type of mixing tends to increase efficiency andreduce costs for the process. The preferred mixing cycle is single stepwherein the polymer, cis-to-trans catalyst, filler, zinc diacrylate, andperoxide are added in sequence.

In one preferred embodiment, the entire core or at least one core layerin a multi-layered structure is formed of a rubber compositioncomprising a material selected from the group of natural and syntheticrubbers including, but not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and combinations of two ormore thereof.

As discussed above, single and multi-layered cores can be made inaccordance with this invention. In two-layered cores, a thermosetmaterial such as, for example, thermoset rubber, can be used to make theouter core layer or a thermoplastic material such as, for example,ethylene acid copolymer containing acid groups that are at leastpartially or fully neutralized can be used to make the outer core layer.Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. Suitable ethylene acid copolymer ionomers and otherthermoplastics that can be used to form the core layer(s) are the samematerials that can be used to make an inner cover layer as discussedfurther below.

In another example, multi-layered cores having an inner core,intermediate core layer, and outer core layer, wherein the intermediatecore layer is disposed between the intermediate and outer core layersmay be prepared in accordance with this invention. More particularly, asdiscussed above, the inner core may be constructed from a thermoplasticor thermoset composition, such as thermoset rubber. Meanwhile, theintermediate and outer core layers also may be formed from thermoset orthermoplastic materials. Suitable thermoset and thermoplasticcompositions that may be used to form the intermediate/outer core layersare discussed above. For example, each of the intermediate and outercore layers may be formed from a thermoset rubber composition. Thus, theintermediate core layer may be formed from a first thermoset rubbercomposition; and the outer core layer may be formed from a secondthermoset rubber composition. In another embodiment, the intermediatecore layer is formed from a thermoset composition; and the outer corelayer is formed from a thermoplastic composition. In a third embodiment,the intermediate core layer is formed from a thermoplastic composition;and the outer core layer is formed from a thermoset composition.Finally, in a fourth embodiment, the intermediate core layer is formedfrom a first thermoplastic composition; and the outer core layer isformed from a second thermoplastic compositions.

In a particular embodiment, the core includes at least one additionalthermoplastic intermediate core layer formed from a compositioncomprising an ionomer selected from DuPont® HPF ESX 367, HPF 1000, HPF2000, HPF AD1035, HPF AD1035 Soft, HPF AD1040, and AD1172 ionomers,commercially available from E. I. du Pont de Nemours and Company. Thecoefficient of restitution (“COW), compression, and surface hardness ofeach of these materials, as measured on 1.55” injection molded spheresaged two weeks at 23° C./50% RH, are given in Table 1 below.

TABLE 1 Solid Sphere Solid Sphere Solid Sphere Shore D Example CORCompression Surface Hardness HPF 1000 0.830 115 54 HPF 2000 0.860 90 47HPF AD1035 0.820 63 42 HPF AD1035 Soft 0.780 33 35 HPF AD 1040 0.855 13560 HPF AD1172 0.800 32 37

Cover Layer Structure

The golf balls of this invention further include an outer cover layermade of a thermoplastic polyurethane composition. In general,polyurethanes contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of a multi-functional isocyanate (NCO—R—NCO)with a long-chain polyol having terminal hydroxyl groups (OH—OH) in thepresence of a catalyst and other additives. The chain length of thepolyurethane prepolymer is extended by reacting it with short-chaindiols (OH—R′—OH). The resulting polyurethane has elastomeric propertiesbecause of its “hard” and “soft” segments, which are covalently bondedtogether. This phase separation occurs because the mainly non-polar, lowmelting soft segments are incompatible with the polar, high melting hardsegments. The hard segments, which are formed by the reaction of thediisocyanate and low molecular weight chain-extending diol, arerelatively stiff and immobile. The soft segments, which are formed bythe reaction of the diisocyanate and long chain diol, are relativelyflexible and mobile. Because the hard segments are covalently coupled tothe soft segments, they inhibit plastic flow of the polymer chains, thuscreating elastomeric resiliency.

By the term, “isocyanate compound” as used herein, it is meant anyaliphatic or aromatic isocyanate containing two or more isocyanatefunctional groups. The isocyanate compounds can be monomers or monomericunits, because they can be polymerized to produce polymeric isocyanatescontaining two or more monomeric isocyanate repeat units. The isocyanatecompound may have any suitable backbone chain structure includingsaturated or unsaturated, and linear, branched, or cyclic. Theseisocyanate compounds also can be referred to as polyisocyanates ormulti-functional isocyanates. By the term, “polyamine” as used herein,it is meant any aliphatic or aromatic compound containing two or moreprimary or secondary amine functional groups. The polyamine compound mayhave any suitable backbone chain structure including saturated orunsaturated, and linear, branched, or cyclic. The term “polyamine” maybe used interchangeably with amine-terminated component. Thesepolyamines also can be referred to as amine compounds ormulti-functional amines. By the term, “polyol” as used herein, it ismeant any aliphatic or aromatic compound containing two or more hydroxylfunctional groups. The term “polyol” may be used interchangeably withhydroxy-terminated component. By the term, “polyimine compound”, it ismeant it is meant any aliphatic or aromatic compound containing two ormore imine functional groups. These polyimines also can be referred toas imine compounds or multi-functional imines.

Thermoplastic polyurethanes have minimal cross-linking; any bonding inthe polymer network is primarily through hydrogen bonding or otherphysical mechanism. Because of their lower level of cross-linking,thermoplastic polyurethanes are relatively flexible. The cross-linkingbonds in thermoplastic polyurethanes can be reversibly broken byincreasing temperature such as during molding or extrusion. That is, thetheremoplastic material softens when exposed to heat and returns to itsoriginal condition when cooled. On the other hand, thermosetpolyurethanes become irreversibly set when they are cured. Thecross-linking bonds are irreversibly set and are not broken when exposedto heat. Thus, thermoset polyurethanes, which typically have a highlevel of cross-linking, are relatively rigid.

Aromatic polyurethanes can be prepared in accordance with this inventionand these materials are preferably formed by reacting an aromaticdiisocyanate with a polyol. Suitable aromatic diisocyanates that may beused in accordance with this invention include, for example, toluene2,4-diisocyanate (TDI), toluene 2,6-diisocyanate (TDI), 4,4′-methylenediphenyl diisocyanate (MDI), 2,4′-methylene diphenyl diisocyanate (MDI),polymeric methylene diphenyl diisocyanate (PMDI), p-phenylenediisocyanate (PPDI), m-phenylene diisocyanate (PDI), naphthalene1,5-diisocynate (NDI), naphthalene 2,4-diisocyanate (NDI), p-xylenediisocyanate (XDI), and homopolymers and copolymers and blends thereof.The aromatic isocyanates are able to react with the hydroxyl or aminecompounds and form a durable and tough polymer having a high meltingpoint. The resulting polyurethane generally has good mechanical strengthand cut/shear-resistance.

Aliphatic polyurethanes also can be prepared in accordance with thisinvention and these materials are preferably formed by reacting analiphatic diisocyanate with a polyol. Suitable aliphatic diisocyanatesthat may be used in accordance with this invention include, for example,isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI),4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI”),meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexanediisocyanate (CHDI), and homopolymers and copolymers and blends thereof.Particularly suitable multi-functional isocyanates include trimers ofHDI or H₁₂ MDI, oligomers, or other derivatives thereof. The resultingpolyurethane generally has good light and thermal stability.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG) which isparticularly preferred, polyethylene propylene glycol, polyoxypropyleneglycol, and mixtures thereof. The hydrocarbon chain can have saturatedor unsaturated bonds and substituted or unsubstituted aromatic andcyclic groups.

In another embodiment, polyester polyols are included in thepolyurethane material. Suitable polyester polyols include, but are notlimited to, polyethylene adipate glycol; polybutylene adipate glycol;polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol;poly(hexamethylene adipate) glycol; and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups. In stillanother embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polycaprolactone polyols include,but are not limited to: 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups. In yet anotherembodiment, polycarbonate polyols are included in the polyurethanematerial of the invention. Suitable polycarbonates include, but are notlimited to, polyphthalate carbonate and poly(hexamethylene carbonate)glycol. The hydrocarbon chain can have saturated or unsaturated bonds,or substituted or unsubstituted aromatic and cyclic groups. In oneembodiment, the molecular weight of the polyol is from about 200 toabout 4000.

There are two basic techniques that can be used to make thepolyurethanes: a) one-shot technique, and b) prepolymer technique. Inthe one-shot technique, the diisocyanate, polyol, andhydroxyl-terminated chain-extender (curing agent) are reacted in onestep. On the other hand, the prepolymer technique involves a firstreaction between the diisocyanate and polyol compounds to produce apolyurethane prepolymer, and a subsequent reaction between theprepolymer and hydroxyl-terminated chain-extender. As a result of thereaction between the isocyanate and polyol compounds, there will be someunreacted NCO groups in the polyurethane prepolymer. The prepolymershould have less than 14% unreacted NCO groups. Preferably, theprepolymer has no greater than 8.5% unreacted NCO groups, morepreferably from 2.5% to 8%, and most preferably from 5.0% to 8.0%unreacted NCO groups. As the weight percent of unreacted isocyanategroups increases, the hardness of the composition also generallyincreases.

Either the one-shot or prepolymer method may be employed to produce thepolyurethane compositions of the invention. In one embodiment, theone-shot method is used, wherein the isocyanate compound is added to areaction vessel and then a curative mixture comprising the polyol andcuring agent is added to the reaction vessel. The components are mixedtogether so that the molar ratio of isocyanate groups to hydroxyl groupsis preferably in the range of about 1.00:1.00 to about 1.10:1.00. In asecond embodiment, the prepolymer method is used. In general, theprepolymer technique is preferred because it provides better control ofthe chemical reaction. The prepolymer method provides a more homogeneousmixture resulting in a more consistent polymer composition. The one-shotmethod results in a mixture that is inhomogeneous (more random) andaffords the manufacturer less control over the molecular structure ofthe resultant composition.

The polyurethane compositions can be formed by chain-extending thepolyurethane prepolymer with a single chain-extender or blend ofchain-extenders as described further below. As discussed above, thepolyurethane prepolymer can be chain-extended by reacting it with asingle chain-extender or blend of chain-extenders. In general, theprepolymer can be reacted with hydroxyl-terminated curing agents,amine-terminated curing agents, and mixtures thereof. The curing agentsextend the chain length of the prepolymer and build-up its molecularweight. In general, thermoplastic polyurethane compositions aretypically formed by reacting the isocyanate blend and polyols at a 1:1stoichiometric ratio. Thermoset compositions, on the other hand, arecross-linked polymers and are typically produced from the reaction ofthe isocyanate blend and polyols at normally a 1.05:1 stoichiometricratio

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds for producing the prepolymer or betweenprepolymer and chain-extender during the chain-extending step.Preferably, the catalyst is added to the reactants before producing theprepolymer. Suitable catalysts include, but are not limited to, bismuthcatalyst; zinc octoate; stannous octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, and tributylamine; organic acids such as oleic acid andacetic acid; delayed catalysts; and mixtures thereof. The catalyst ispreferably added in an amount sufficient to catalyze the reaction of thecomponents in the reactive mixture. In one embodiment, the catalyst ispresent in an amount from about 0.001 percent to about 1 percent, andpreferably 0.1 to 0.5 percent, by weight of the composition.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”); andmixtures thereof. One particularly suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When the polyurethane prepolymer is reacted with hydroxyl-terminatedcuring agents during the chain-extending step, as described above, theresulting polyurethane composition contains urethane linkages. On theother hand, when the polyurethane prepolymer is reacted withamine-terminated curing agents during the chain-extending step, anyexcess isocyanate groups in the prepolymer will react with the aminegroups in the curing agent. The resulting polyurethane compositioncontains urethane and urea linkages and may be referred to as apolyurethane/urea hybrid. The concentration of urethane and urealinkages in the hybrid composition may vary. In general, the hybridcomposition may contain a mixture of about 10 to 90% urethane and about90 to 10% urea linkages.

More particularly, when the polyurethane prepolymer is reacted withhydroxyl-terminated curing agents during the chain-extending step, asdescribed above, the resulting composition is essentially a purepolyurethane composition containing urethane linkages having thefollowing general structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons.

However, when the polyurethane prepolymer is reacted with anamine-terminated curing agent during the chain-extending step, anyexcess isocyanate groups in the prepolymer will react with the aminegroups in the curing agent and create urea linkages having the followinggeneral structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons.

The polyurethane compositions used to form the cover layer may containother polymer materials including, for example: aliphatic or aromaticpolyurethanes, aliphatic or aromatic polyureas, aliphatic or aromaticpolyurethane/urea hybrids, olefin-based copolymer ionomer compositions,polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, available from DuPont;polyurethane-based thermoplastic elastomers, such as Elastollan®,available from BASF; polycarbonate/polyester blends such as Xylex®,available from SABIC Innovative Plastics; maleic anhydride-graftedpolymers such as Fusabond®, available from DuPont; and mixtures of theforegoing materials.

In addition, the polyurethane compositions may contain fillers,additives, and other ingredients that do not detract from the propertiesof the final composition. These additional materials include, but arenot limited to, catalysts, wetting agents, coloring agents, opticalbrighteners, cross-linking agents, whitening agents such as titaniumdioxide and zinc oxide, ultraviolet (UV) light absorbers, hindered aminelight stabilizers, defoaming agents, processing aids, surfactants, andother conventional additives. Other suitable additives includeantioxidants, stabilizers, softening agents, plasticizers, includinginternal and external plasticizers, impact modifiers, foaming agents,density-adjusting fillers, reinforcing materials, compatibilizers, andthe like. Some examples of useful fillers include zinc oxide, zincsulfate, barium carbonate, barium sulfate, calcium oxide, calciumcarbonate, clay, tungsten, tungsten carbide, silica, and mixturesthereof. Rubber regrind (recycled core material) and polymeric, ceramic,metal, and glass microspheres also may be used. Generally, the additiveswill be present in the composition in an amount between about 1 andabout 70 weight percent based on total weight of the compositiondepending upon the desired properties.

Treatment of Thermoplastic Polyurethane Cover

The golf ball having the molded thermoplastic polyurethane cover can bepost-treated with a composition comprising an epoxy-functional compoundsuch as, for example, glycidyl methacrylate, glycidyl acrylate,diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F,1,4-cyclohexanedimethanol diglycidyl ether, 1,4-butanediol diglycidylether, trimethylolpropane triglycidyl ether; and mixtures thereof. Then,the treated cover can be treated with an epoxy curing agent such as, forexample, amines, acids, anhydrides, imines, isocyanates, and hydroxyls,and mixtures thereof. Different methods for applying the compositionscan be used including, for example, spraying, dipping, brushing, androlling.

The compositions can contain a suitable solvent. Any solvent that canform a solution, dispersion, suspension, and the like with theepoxy-functional compounds or epoxy curing agents can be used.Preferably, the solvent allows for some level of penetration of thecompound into the thermoplastic polyurethane substrate to which it isapplied. Suitable solvents include, for example, toluene, xylene,naphthalene, ketones, and acetates. Preferably, the solvent is selectedfrom the group consisting of acetone, methyl ethyl ketone, methyl amylketone, dimethyl heptanone, methyl pentanone, methyl isobutyl ketone,cyclohexanone, methyl acetate, ethyl acetate, and butyl acetate, andmixtures thereof.

In one embodiment, an outer cover layer is formed over the golf ballsub-assembly, wherein the outer cover layer is formed from a firstcomposition comprising a thermoplastic polyurethane. A secondcomposition comprising an epoxy-functional compound is applied to thecover layer. The second composition can contain an epoxy curing agent.For example, a golf ball having a thermoplastic polyurethane cover canbe dipped in a bath containing an epoxy-functional compound for asuitable period of time, for example, about 1 to about 60 minutes. Inone example, the ball is dipped and held in the bath for about 1 toabout 30 minutes, or about 1 to about 15 minutes, or about 1 to about 10minutes. In another example, the ball is dipped and held in the bath forabout 2 to about 12 minutes, or about 2 to about 10 minutes, or about 3to about 8 minutes. In yet another embodiment, the ball is dipped andheld in the bath for at least about 5 minutes. Then, the balls arerinsed in a suitable rinsing solution such as acetone before beingheated to promote cross-linking. For example, the balls can be heated ata temperature of about 120° F. to about 200° F., or about 130° F. toabout 190° F., or about 140° F. to about 160° F. The balls are heatedfor a sufficient period of time, for example, about 1 to about 24 hours,or about 2 to about 20 hours, or about 3 to about 12 hours, or about 4to about 10 hours.

In a second embodiment, an epoxy-containing thermoplastic polyurethanecomposition first can be made by blending a thermoplastic polyurethanewith an epoxy-functional compound. Then, the epoxy-containingthermoplastic polyurethane composition can be molded to form a golf ballouter cover. Next, the molded thermoplastic polyurethane cover istreated with a composition comprising an epoxy curing agent to form atleast a partially cross-linked cover. For example, a golf ball having acover made from a composition comprising a thermoplastic polyurethaneand epoxy-functional compound can be made. Next, the ball is dipped in abath containing an epoxy-curing agent for a suitable period of time, forexample, about 1 to about 60 minutes. In one example, the ball is dippedand held in the bath for about 1 to about 30 minutes, or about 1 toabout 15 minutes, or about 1 to about 10 minutes. In another example,the ball is dipped and held in the bath for about 2 to about 12 minutes,or about 2 to about 10 minutes, or about 3 to about 8 minutes. In yetanother embodiment, the ball is dipped and held in the bath for at leastabout 5 minutes. Then, the balls are rinsed in a suitable rinsingsolution such as acetone before being heated to promote cross-linking.For example, the balls can be heated at a temperature of about 120° F.to about 200° F., or about 130° F. to about 190° F., or about 140° F. toabout 160° F. The balls are heated for a sufficient period of time, forexample, about 1 to about 24 hours, or about 2 to about 20 hours, orabout 3 to about 12 hours, or about 4 to about 10 hours.

More particularly, in one example, the epoxy-functional compound ispre-blended with thermoplastic polyurethane (TPU) pellets prior toinjection-molding the golf ball cover. This step can be performed, forexample, by coating, spraying, or soaking the TPU pellets in theepoxy-functional compound. The epoxy-functional compound also can beintroduced in the form of a masterbatch or dispersion. The TPU/epoxyblend is then injection-molded about the core subassembly to form thecover. The molded cover is then exposed to a solution of epoxy curingagent such as, for example, hydroxyls, isocyanates, amines, acids, oranhydrides as described further below, which can react with theepoxy-functional compound.

In a further embodiment, an epoxy-containing thermoplastic polyurethanecomposition first can be made by blending a thermoplastic polyurethanewith an epoxy curing agent. Then, the thermoplastic polyurethanecomposition can be molded to form a golf ball outer cover. Next, themolded thermoplastic polyurethane cover is treated with a compositioncomprising an epoxy-functional compound to form at least a partiallycross-linked cover. For example, a golf ball having a cover made from acomposition comprising a thermoplastic polyurethane and epoxy-curingagent can be made. Next, the ball is dipped in a bath containing anepoxy-functional compound for a suitable period of time, for example,about 1 to about 60 minutes. In one example, the ball is dipped and heldin the bath for about 1 to about 30 minutes, or about 1 to about 15minutes, or about 1 to about 10 minutes. In another example, the ball isdipped and held in the bath for about 2 to about 12 minutes, or about 2to about 10 minutes, or about 3 to about 8 minutes. In yet anotherembodiment, the ball is dipped and held in the bath for at least about 5minutes. Then, the balls are rinsed in a suitable rinsing solution suchas acetone before being heated to promote cross-linking. For example,the balls can be heated at a temperature of about 120° F. to about 200°F., or about 130° F. to about 190° F., or about 140° F. to about 160° F.The balls are heated for a sufficient period of time, for example, about1 to about 24 hours, or about 2 to about 20 hours, or about 3 to about12 hours, or about 4 to about 10 hours.

In yet another embodiment, three compositions are used in producing theouter cover. First, an outer cover layer is formed over the golf ballsub-assembly, wherein the outer cover layer is formed from a firstcomposition comprising a thermoplastic polyurethane. A secondcomposition comprising an epoxy-functional compound is applied to thecover layer. Then, a third composition comprising an epoxy curing agentis applied to the cover to form at least a partially cross-linked cover.

As discussed above, in one embodiment, an epoxy-containing thermoplasticpolyurethane cover is made, and then the molded cover is exposed to anepoxy curing agent such as isocyanates. For example, themulti-functional isocyanate compound can be selected from the groupconsisting of toluene 2,4-diisocyanate (TDI), toluene 2,6-diisocyanate(TDI), 4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylenediphenyl diisocyanate (MDT), polymeric methylene diphenyl diisocyanate(PMDT), p-phenylene diisocyanate (PPDI), m-phenylene diisocyanate (PDI),naphthalene 1,5-diisocynate (NDI), naphthalene 2,4-diisocyanate (NDI),p-xylene diisocyanate (XDI), and isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDT”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI), and homopolymers and copolymersand blends thereof. Preferably, the polyisocyanate is selected from thegroup consisting of 4,4′-methylene diphenyl diisocyanate (MDT),2,4′-methylene diphenyl diisocyanate (MDT), toluene 2,4-diisocyanate(TDI), toluene 2,6-diisocyanate (TDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), p-phenylene diisocyanate (PPDI), andisophorone diisocyanate (IPDI), and homopolymers and copolymers andblends thereof.

AS described in Gan et al., US Patent Application Publication US2010/0237292, the reaction of the multi-functional isocyanate compoundand multi-functional epoxy resin incorporates the isocyanate groups fromthe multi-functional isocyanate compound into the multi-functional epoxyresin backbone to form a poly-oxazolidone structure. This product alsocan be referred to as an oxazolidone ring-containing epoxy resin. Theformation of the poly-oxazolidone structure within the multi-functionalepoxy resin backbone increases the molecular weight of themulti-functional epoxy resin, and thus increases the softening point ofthe resin. The Tg of the resin cross-linked resin is also higher becausethe addition of the poly-oxazolidone structure into the multi-functionalepoxy resin backbone increases both the epoxy backbone structurestiffness and the epoxy cross-linking density.

Another mechanism for the reaction of epoxides with isocyanates isdisclosed in Marten et al., U.S. Pat. No. 5,977,286. Epoxy resincompositions containing polyepoxides having at least two 1,2-epoxidegroups are disclosed. The polyepoxides can be obtained by reacting (i)di- or polyepoxides or mixtures thereof with monoepoxides, (ii) one ormore amines chosen from sterically hindered amines, disecondary diaminesand diprimary diamines to form an epoxide-amine adduct, and (iii)subsequently reacting the epoxide-amine adduct with polyfunctionalisocyanates. The composition also contains curing agents for thepolyepoxides and can optionally contain additional 1,2-epoxide compoundsand additives.

The thermoplastic polyurethane cover may be treated one or more timeswith epoxy curing agents such as isocyanates. In addition, ahydroxyl-functional material such as an oligomer or polymer may be addedto the composition cover (in an excess amount over the polyol contentused to form the thermoplastic polyurethane composition.) Thisultimately provides additional hydroxyl sites for reacting withisocyanates in post-molding steps. Suitable hydroxyl-functionalmaterials include, for example, those described above and thosedisclosed as polyahls in Parnell, U.S. Pat. No. 9,321,201 andpolyester-based polyols, diamines, polybutadiene based polyols,polyamines, diacids, polyacids and mixtures thereof as disclosed inMelanson et al., U.S. Pat. No. 7,842,211.

The thermoplastic polyurethane composition can be furthertreated/exposed to a catalyst (typically an organotin compound in asolvent) as disclosed in Parnell, U.S. Pat. Nos. 9,566,728 and8,551,567. Such catalysts will push or promote the reactions describedabove. PCT International Application Publication WO 91/18937A1 (E.I. duPont de Nemours and Company) describes the use of 1,3-disubstitutedimidazole-2-thiones as catalysts for crosslinking epoxy functionalizedmaterials with isocyanate functionalized materials. Other suitablecatalysts include, for example, those selected from the group consistingof dibutyl tin dilaurate, dibutyl tin acetylacetonate, dibutyl tindibutoxide, dibutyl tin sulphide, dibutyl tin di-2-ethylhexanoate,dibutyl tin (IV) diacetate, dialkyltin (IV) oxide, tributyl tinlaurylmercaptate, dibutyl tin dichloride, organo lead, tetrabutyltitanate, tertiary amines, mercaptides, stannous octoate, potassiumoctoate, zinc octoate, diazo compounds, and potassium acetate, andmixtures thereof.

In another embodiment, the above-described molded golf ball having theepoxy-containing thermoplastic polyurethane cover is treated with apolyol (such as butanediol.) Other suitable polyols that can be used totreat the epoxy-containing thermoplastic polyurethane cover arediscussed above. Then, the golf ball is exposed to a solution ofisocyanate and/or epoxy curative also as discussed above. The freehydroxyl groups are able to react with the isocyanate groups and epoxycuring agent.

In still another embodiment, the above-described molded golf ball havingthe epoxy-containing thermoplastic polyurethane cover composition has anexcess amount of polyol groups (that is, the polyurethane composition isisocyanate under-indexed—the composition preferably has an isocyanateindex of less than 96. Indexing of the isocyanate groups is discussedfurther below.) This golf ball is then exposed to a solution ofisocyanate or epoxy curative as discussed above. In yet anotherembodiment, the above-described molded golf ball having thethermoplastic polyurethane cover composition has an excess amount ofisocyanate groups (that is, the polyurethane composition is isocyanateover-indexed—the composition preferably has an isocyanate index of atleast 115.) This golf ball is then exposed to a solution of isocyanateor epoxy curative as discussed above.

Epoxy-Functional Compounds

In general, epoxy-functional compounds contain epoxide groups having thefollowing structure:

These epoxy-functional compounds are also commonly referred to asepoxide-functional compounds or epoxy resins. One type of epoxy resin ismade from epichlorohydrin and bisphenol A. Aliphatic polyols such asglycerol can be used instead of the aromatic bisphenol A. These reactiveepoxies form a tight, cross-linked polymer network having goodmechanical properties and high temperature and chemical-resistance. Theepoxy resins are reacted with a co-reactant (commonly referred to as acuring agent or hardener) to form a thermoset material. Epoxy curingagents are known in the art and include, for example, polyfunctionalamines, acids, acid anhydrides, phenols, alcohols, and thiols. “Hawley'sCondensed Chemical Dictionary” (ed. Richard L. Lewis, Sr. (New York:John Wiley & Sons, Inc., 1997).

Any suitable epoxy-functional oligomer, polymer, copolymer, or othermaterial can be included in the thermoplastic polyurethane compositionof this invention. Examples of epoxy resins that can be used inaccordance with the present invention include bisphenol epoxy resins.aliphatic epoxy resins, novolac epoxy resins, brominated epoxy resins,isocyanurate epoxy resins, and the like. For example, an oligomer orpolymer having a glycidyl functionality such as glycidyl (meth)acrylateor glycidyl acrylate can be used. A commercially-available modifiedpolyolefinic material, which is sold under the tradename, Lotader™ byArkema (such as Lotader™ AX8700) or Elvaloy™ ethyleneacrylate-glycidylmethacrylate polymers also can be used. Also, a glycidyl functionalacrylic resin cross-linker such as GMA-500TH sold by Estron Chemical,can be used. Epon™ (available from Hexion), DER™ (available from DowChemical Co.), Araldite™ (available from CIBA GEIGY Co.), and Epi-Rez™(available from Hoechst-Celanese Corporation). Other suitableepoxy-functional compounds include diglycidyl ether of bisphenol A (forexample, EPON 828 available from Hexion); diglycidyl ether of bisphenolF (for example, EPON 862 available from Hexion);1,4-cyclohexanedimethanol diglycidyl ether (for example, HELOXY107available from Hexion); 1,4-butanediol diglycidyl ether (for example,HELOXY 67 available from Hexion); and trimethylolpropane triglycidylether (for example, HELOXY 48 available from Hexion). Additionally,epoxy-functional ethylene propylene rubbers (“EPR”),ethylene-propylene-diene (“EPDM”) rubbers, styrenic block copolymerrubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where“S” is styrene, “I” is isobutylene, and “B” is butadiene) and the likemay be used or any copolymer of glycidyl methacrylate and alky acrylate(e.g., enba-gma) can be used. Epoxidized polyethers or polyesters alsocan be used. In addition, a di, oligomeric or polyepoxide compound alsomay be used such as diepoxybutane, aliphatic or cycloaliphatic epoxide,diglycidyl ether of bisphenol-A (DGEBA). The reaction betweendiisocyanates and diepoxides can produce polyoxazolidones. However, thereaction may be accompanied by concurrent cyclization of isocyanate toproduce trimeric isocyanurate.

Still other suitable epoxy-functional compounds that can be used inaccordance with this invention are trifunctional glycidyl amine basedepoxy resins sold by Huntsman as Araldite MY 0500, 0510, 0600 and Tactix742. Also, tetrafunctional amine epoxies such as, for example, thosesupplied by Huntsman and sold under the tradenames, Araldite MY 721&725, XB 9721, MY 9512, MY 9634, 9655, 9663 and 9612, can be used. Othersuitable epoxies include: a) aliphatic and cycloaliphatic glycidyl anddiglycidyl ethers sold by Huntsman as Araldite CY or DY; b) bisphenol-Aliquid epoxy resins (modified and unmodified) sold under the tradenames,Araldite or Tactix including Araldite GY, MY, LY, CT, GT, LT or GZ; c)bisphenol-F based epoxy resins such as Araldite GY or PY; and d) epoxyphenol novalacs and epoxy cresol novolacs.

Epoxy Curing Agents

The thermoplastic polyurethane composition comprising the epoxy resin istreated with an epoxy curing agent to effectively cure the epoxy resin.The epoxy curing agent can be added before, during, or after treatmentof the molded thermoplastic polyurethane cover. Examples of suitableepoxy curing agents are, for example, amine-liberating thermoplastics,amines, imines, acids, anhydrides, and isocyanates. For example, anamine-terminated thermoplastic polyamide resin can be used as the curingagent. In one example, a thermoplastic polyurethane compositioncontaining the epoxy-functional compound is prepared and the compositionis molded into the cover as described above. The epoxy-containingthermoplastic polyurethane cover is then treated with an epoxy curingagent. The shaped cover is allowed to cross-link at room temperature orby using heat to accelerate curing. Thus, the polyurethane compositionis thermoplastic in nature prior to addition of the epoxy curing agent.After adding the epoxy curing agent, the composition is cross-linked andthis increases the physical and mechanical properties of thecomposition, for example, there is higher tensile strength, greaterhardness, and higher temperature-resistance.

As described in Czerwinski et al., U.S. Pat. No. 4,870,142, othersuitable epoxy curing agents include, for example, polyamines,polyamides, anhydrides, Lewis acids, mercaptans and the like. Forexample, polysebacic polyanhydride, nadic methyl anhydride, and thefollowing products available from Ciba Geigy Co.: HT 939™ (a polyamidetype curing agent having a curing temperature of about 120° C.; HY 920™(a liquid non-aromatic anhydride having a curing temperature of about170° C.); and DY 9577™ (an amine complex having a curing temperature ofabout 170° C.) can be used. The amount of curing agent used depends uponthe type of curing agent and the epoxy value and can easily bedetermined by one skilled in the art based on the weight of the epoxyresin(s) in the thermoplastic composition. Thus, the amount of thecuring agent is stoichiometric or greater based on the epoxyfunctionality in the thermoplastic composition.

In one preferred embodiment, aliphatic amines are used as the epoxycuring agent. For example, primary amines such as diethylene triamine(DETA), triethylene tetramine (TETA), tetraethylenepentamine (TEPA),N-aminoethyl-piperazine (N-AEP), and meta-xylenediamines (MXDA) can beused. Polyetheramines, such as Jeffamines™ (available from Huntsman,Inc.) can be used. Tertiary amines (Lewis bases) also can be used.Cycloaliphatic amines such as isophoronediamine (IPDA) andmethylene-di(cyclohexylamine) (PACM) also can be used. Other epoxycuring agents include polyamides or amide/imidazolines and anhydrides.Radiation-curable epoxy resins also can be used and radiation sourcessuch as ultraviolet (UV)-light, infrared (IR), and electron beam (EB)systems can be used to cure the material as described in Lee et al.,U.S. Pat. No. 6,376,638.

When an amine is used as the epoxy curing agent, the curing reactioninvolves a two-stage reaction, wherein a primary amine group reacts withepoxy groups to provide secondary amine groups as shown in Reaction (a)below; and secondary amine groups further react with the epoxy groupsand generate tertiary amine groups as shown in Reaction (b) below:

In other embodiments, the epoxy-containing thermoplastic polyurethanecomposition can be made by blending in situ a thermoplastic polyurethanewith an epoxy-functional compound and epoxy curing agent.

Intermediate Layers

In one preferred embodiment, an intermediate layer is disposed betweenthe single or multi-layered core and surrounding cover layer. Theseintermediate layers also can be referred to as casing or inner coverlayers. The intermediate layer can be formed from any materials known inthe art, including thermoplastic and thermosetting materials, butpreferably is formed of an ionomer composition comprising an ethyleneacid copolymer containing acid groups that are at least partiallyneutralized. Suitable ethylene acid copolymers that may be used to formthe intermediate layers are generally referred to as copolymers ofethylene; C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylicacid; and optional softening monomer. These ethylene acid copolymerionomers also can be used to form the inner core and outer core layersas described above.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized. Preferred ionomers are salts of O/X- andO/X/Y-type acid copolymers, wherein O is an α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer. O is preferably selected from ethylene and propylene. X ispreferably selected from methacrylic acid, acrylic acid, ethacrylicacid, crotonic acid, and itaconic acid. Methacrylic acid and acrylicacid are particularly preferred. Y is preferably selected from (meth)acrylate and alkyl (meth) acrylates wherein the alkyl groups have from 1to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl(meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/isobutyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α,β-ethylenically unsaturated mono- ordicarboxylic acid in the acid copolymer is typically from 1 wt. % to 35wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %, basedon total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed in U.S.Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference. The acid copolymer can be reacted withthe optional high molecular weight organic acid and the cation sourcesimultaneously, or prior to the addition of the cation source. Suitablecation sources include, but are not limited to, metal ion sources, suchas compounds of alkali metals, alkaline earth metals, transition metals,and rare earth elements; ammonium salts and monoamine salts; andcombinations thereof. Preferred cation sources are compounds ofmagnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals.

Other suitable thermoplastic polymers that may be used to form theintermediate layer include, but are not limited to, the followingpolymers (including homopolymers, copolymers, and derivatives thereof:(a) polyester, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (b) polyamides, polyamide-ethers, andpolyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,6,001,930, and 5,981,654, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof; (c)polyurethanes, polyureas, polyurethane-polyurea hybrids, and blends oftwo or more thereof; (d) fluoropolymers, such as those disclosed in U.S.Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (e) polystyrenes, such as poly(styrene-co-maleicanhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate),polyethylene styrene, and blends of two or more thereof; (f) polyvinylchlorides and grafted polyvinyl chlorides, and blends of two or morethereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the core and intermediate layers in accordance withthis invention. For example, thermoplastic polyolefins such as linearlow density polyethylene (LLDPE), low density polyethylene (LDPE), andhigh density polyethylene (HDPE) may be cross-linked to form bondsbetween the polymer chains. The cross-linked thermoplastic materialtypically has improved physical properties and strength overnon-cross-linked thermoplastics, particularly at temperatures above thecrystalline melting point. Preferably a partially or fully-neutralizedionomer, as described above, is covalently cross-linked to render itinto a thermoset composition (that is, it contains at least some levelof covalent, irreversible cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Modifications in thermoplastic polymeric structure of thermoplastic canbe induced by a number of methods, including exposing the thermoplasticmaterial to high-energy radiation or through a chemical process usingperoxide. Radiation sources include, but are not limited to, gamma-rays,electrons, neutrons, protons, x-rays, helium nuclei, or the like. Gammaradiation, typically using radioactive cobalt atoms and allows forconsiderable depth of treatment, if necessary. For core layers requiringlower depth of penetration, electron-beam accelerators or UV and IRlight sources can be used. Useful UV and IR irradiation methods aredisclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, which areincorporated herein by reference. The thermoplastic core layers may beirradiated at dosages greater than 0.05 Mrd, preferably ranging from 1Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and most preferablyfrom 4 Mrd to 10 Mrd. In one preferred embodiment, the cores areirradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

Golf Ball Construction

The solid cores for the golf balls of this invention may be made usingany suitable conventional technique such as, for example, compression orinjection-molding. Typically, the cores are formed by compressionmolding a slug of uncured or lightly cured rubber material into aspherical structure. Prior to forming the cover layer, the corestructure may be surface-treated to increase the adhesion between itsouter surface and adjacent layer. Such surface-treatment may includemechanically or chemically-abrading the outer surface of the core. Forexample, the core may be subjected to corona-discharge,plasma-treatment, silane-dipping, or other treatment methods known tothose in the art. The cover layers are formed over the core or ballsub-assembly (the core structure and any intermediate layers disposedabout the core) using any suitable method as described further below.Prior to forming the cover layers, the ball sub-assembly may besurface-treated to increase the adhesion between its outer surface andthe overlying cover material using the above-described techniques.

Conventional compression and injection-molding and other methods can beused to form cover layers over the core or ball sub-assembly. Ingeneral, compression molding normally involves first making half(hemispherical) shells by injection-molding the composition in aninjection mold. This produces semi-cured, semi-rigid half-shells (orcups). Then, the half-shells are positioned in a compression mold aroundthe core or ball sub-assembly. Heat and pressure are applied and thehalf-shells fuse together to form a cover layer over the core orsub-assembly. Compression molding also can be used to cure the covercomposition after injection-molding. For example, a thermally-curablecomposition can be injection-molded around a core in an unheated mold.After the composition is partially hardened, the ball is removed andplaced in a compression mold. Heat and pressure are applied to the balland this causes thermal-curing of the outer cover layer.

Retractable pin injection-molding (RPIM) methods generally involve usingupper and lower mold cavities that are mated together. The upper andlower mold cavities form a spherical interior cavity when they arejoined together. The mold cavities used to form the outer cover layerhave interior dimple cavity details. The cover material conforms to theinterior geometry of the mold cavities to form a dimple pattern on thesurface of the ball. The injection-mold includes retractable supportpins positioned throughout the mold cavities. The retractable supportpins move in and out of the cavity. The support pins help maintain theposition of the core or ball sub-assembly while the molten compositionflows through the mold gates. The molten composition flows into thecavity between the core and mold cavities to surround the core and formthe cover layer. Other methods can be used to make the cover including,for example, reaction injection-molding (RIM), liquid injection-molding,casting, spraying, powder-coating, vacuum-forming, flow-coating,dipping, spin-coating, and the like.

As discussed above, an inner cover layer or intermediate layer,preferably formed from an ethylene acid copolymer ionomer composition,can be formed between the core or ball sub-assembly and cover layer. Theintermediate layer comprising the ionomer composition may be formedusing a conventional technique such as, for example, compression orinjection-molding. For example, the ionomer composition may beinjection-molded or placed in a compression mold to produce half-shells.These shells are placed around the core in a compression mold, and theshells fuse together to form an intermediate layer. Alternatively, theionomer composition is injection-molded directly onto the core usingretractable pin injection-molding.

Application of Primer and Top-Coats

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, and application of coatings in accordance with this invention.

For example, in traditional white-colored golf balls, thewhite-pigmented outer cover layer may be surface-treated using asuitable method such as, for example, corona, plasma, or ultraviolet(UV) light-treatment. In another finishing process, the golf balls arepainted with one or more paint coatings. For example, white or clearprimer paint may be applied first to the surface of the ball and thenindicia may be applied over the primer followed by application of aclear polyurethane top-coat. Indicia such as trademarks, symbols, logos,letters, and the like may be printed on the outer cover or prime-coatedlayer, or top-coated layer using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Any of the surfacecoatings may contain a fluorescent optical brightener.

In one embodiment, a first (primer) polyurethane coating comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 is applied to the outer cover. The golf ball is thenpreferably treated with heat so the coating is at least partially-cured.For example, the golf ball can be heated preferably to a surfacetemperature of at least about 105° to about 200° F. Preferably, the golfball is heated to a surface temperature of about 120° to about 150° F.Preferably, the golf ball is then heated for at a period of 2 minutes toabout 240 minutes, more preferably a period of 4 minutes to 120 minutes,and most preferably about 8 minutes to 60 minutes. In a third step, asecond (top-coat) polyurethane coating is applied to the outer cover.Any suitable coating technique may be used to apply the first and secondpolyurethane coatings. For example, spraying, dipping, brushing, orrolling methods can be used. Then the golf ball can go through a seriesof finishing steps.

In a second embodiment, a first (primer) polyurethane comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 is applied to the outer cover and the golf ball is treatedwith heat as described above. In a third step, a second (top-coat)polyurethane coating having an isocyanate index of less than 96 isapplied to the outer cover.

In a third embodiment, a first (primer) polyurethane comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 and further comprising a catalyst is applied to the outercover and the golf ball is treated with heat as described above. In athird step, a second (top-coat) polyurethane coating is applied to theouter cover as described above. The thermoplastic polyurethanecomposition of the outer cover layer and second (top-coat) polyurethanecoatings also may comprise catalysts. Suitable catalysts include, forexample, dibutyl tin dilaurate, dibutyl tin acetylacetonate, dibutyl tindibutoxide, dibutyl tin sulphide, dibutyl tin di-2-ethylhexanoate,dibutyl tin (IV) diacetate, dialkyltin (IV) oxide, tributyl tinlaurylmercaptate, dibutyl tin dichloride, organo lead, tetrabutyltitanate, tertiary amines, mercaptides, stannous octoate, potassiumoctoate, zinc octoate, diazo compounds, and potassium acetate, andmixtures thereof.

In a fourth embodiment, a mixture comprising a multi-functionalisocyanate and solvent is applied to the outer cover and the golf ballis treated with heat as described above. The mixture also may containadditives such as, for example, ultraviolet (UV) light stabilizers. Afirst (primer) polyurethane coating that may be over-indexed orunder-indexed may be applied to the outer cover. For example, themixture may be over-indexed and comprise unreacted isocyanate groups andhave an isocyanate index of at least about 115. In another example, themixture may be under indexed and have an isocyanate index of less than96. The golf ball is treated with heat as described above. A secondpolyurethane top-coating having an isocyanate index that is over-indexedor under-indexed may be applied. This treatment of the outer cover layerwith isocyanates further enhances cross-linking and improves coverdurability. These isocyanates can function as cross-linkers in thethermoplastic polyurethane cover. The chain length of the thermoplasticpolyurethane is extended and thus the molecular weight of thepolyurethane is increased when treated with the multi-functionalisocyanates.

Preferably, the multi-functional isocyanate compound is selected fromthe group consisting of toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocynate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and isophoronediisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI),4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI”),meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexanediisocyanate (CHDI), and homopolymers and copolymers and blends thereof.More preferably, the polyisocyanate is selected from the groupconsisting of 4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylenediphenyl diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-dicyclohexylmethane diisocyanate (“H₁₂MDI”), p-phenylene diisocyanate (PPDI), and isophorone diisocyanate(IPDI), and homopolymers and copolymers and blends thereof.

The solvent may be any solvent that forms a solution with themulti-functional isocyanate and allows for some level of penetration ofthe isocyanate into the thermoplastic polyurethane substrate to which itis applied. Suitable solvents include, for example, toluene, xylene,naphthalene, ketones, and acetates. Preferably, the solvent comprisesone selected from the group consisting of acetone, methyl ethyl ketone,methyl amyl ketone, dimethyl heptanone, methyl pentanone, methylisobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, and butylacetate, and mixtures thereof. The mixture preferably comprises fromabout 1 to 25 wt. % isocyanate, and more preferably about 2 to 20 wt. %,and most preferably 5 to 18 wt % isocyanate.

Polyurethane Coatings and Isocyanate Index

Generally, the polyurethane coating material may be a two-part coatingsystem. A preferred coating system includes (1) a first part comprisinga polyol or another compound containing an active hydrogen atom, and (2)a second part comprising a polyisocyanate (or polyisocyanurate) with atleast two —N═C═O groups.

Suitable polyols for the polyurethane coating system include bothpolyether and polyester polyols. In one particular embodiment, thepolyol may be a hydroxyl functional polyol having a hydroxyl equivalentweight in the range of from about 50 to about 1500, or an hydroxylequivalent weight being in the range of from about 200 to about 800.Suitable polyesters for use herein include poly (oxydiethylene adipates)that are condensation products of diethylene glycol and adipic acid,branched with trimethylolpropane or pentaerythritol, andpolycaprolactone (hydroxycaproic acid) polyesters.

Suitable polyethers include polymers of propylene oxide or propyleneoxide/ethylene oxide. Such materials are usually triols or diols withmolecular weights between 1000 and 7000. Suitable examples of polyolsinclude Desmophen™ 651A-65, 800, 670A-80, 680-70 and 631A-75, which aresaturated polyester resins, commercially available from Bayer Corp.

As mentioned above, in addition to a polyol, the two-part polyurethanesystem also comprises a polyisocyanate (or polyisocyanurate) with atleast two —N═C═O groups, carried in a solvent. Various diisocyantes,including but not limited to hexamethylene diisocyanate (HDI), methylenediisocyanate (MDI), toluene diisocyanate (TDI), and isophoronediisocyanate (IPDI) may be used. In particular embodiments, aliphaticisocyanates may be used. HDI derivatives contemplated for use herein aresold by Bayer Corp. under the trademark, Desmodur™. One such compositionis Desmodur™ N-3200, which is a low viscosity biuret of HDI.

The polyisocyanate used herein may have an equivalent weight within therange of from about 100 to about 1,200, or from about 150 to about 300in some embodiments. The polyisocyanate may be carried in a solvent,with the solvent solution containing from a minimum of about 40%,alternatively about 60%, alternatively about 70%, to a maximum ofapproaching 100%, and in particular about 85%, by weight of thepolyisocyanate.

Suitable solvents for the polyisocyanate include methyl isobutyl ketone,methyl amyl ketone, methyl isoamyl ketone, butyl acetate and propyleneglycol monomethyl ether acetate, or mixtures thereof. In a particularlyembodiment, the solvent is present in an amount of 20-65 weight %, or inamount of 40-60 weight % based upon the total weight of the coatingsystem. Urethane grade solvents (i.e. low-moisture solvents) may be usedin particular embodiments.

The polyurethane coating material may also be formed from a polyurethanesystem that includes a catalyst. Generally, the catalyst increases therate of curing. The catalyst may comprise at least one member selectedfrom the group consisting of dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diazo compounds, and potassiumacetate.

The catalyst may be present in a quantity of 0.01-10 weight activecatalyst (not including any carrier) based on total resin solids (polyolplus polyisocyanate, excluding solvents). The quantity of catalyst willdepend upon the type of catalyst, polyol, polyisocyanate, and solventswhich are used, as well as the curing temperature and desired curingtime. For example, when dibutyl tin dilaurate is used as the catalyst,it preferably is present in an amount of about 0.05-0.35 weight % activecatalyst based upon total resin solids, and more preferably 0.08-0.15weight % based upon total resin solids. Generally, the catalystpreferably is present in an amount sufficient to reduce the curing timeof the coating as compared to a coating system which does not containthe catalyst but is otherwise identical.

Any aromatic or aliphatic or blend thereof may be used includingpolyisocyanates. Preferred examples of the isocyanate component in thepolyurethane include: aromatic polyisocyanates such as 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluenediisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI),tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate(PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethanediisocyanate (HINDI), hydrogenated xylylene diisocyanate (H₆XDI) andisophorone diisocyanate (IPDI); and aliphatic polyisocyanates such ashexamethylene diisocyanate (HDI). Two or more polyisocyanates may beused in combination. In light of the weather resistance, TMXDI, XDI,HDI, H₆XDI, IPDI and H₁₂MDI are preferred.

As also noted herein, it has been discovered that as the melt index of apolymer increases, some of the physical properties of the polymerdecrease. As a result, in the more preferred embodiments of theinvention the high melt index golf ball components are further treatedwith a liquid isocyanate solution. By performing an isocyanatepost-molding treatment process to the golf ball, the physical propertiesof the thermoplastic polyurethane, polyurea or polyurethane/polyureacover material may not only increase, but may increase beyond the valuesof the non-refined material. This physical property improvement yields asignificant improvement in golf ball durability, namely improved cut andscuff (groove shear) resistance.

This post-application of isocyanate is believed to allow for the use ofrelatively high melt index thermoplastic polyurethane, polyurea orpolyurethanes/polyureas to be used in conventional injection moldingmachines and/or in reaction injection molding (“RIM”) equipment to moldthin wall layers, i.e. 0.075 inches, more preferably 0.050 inches andbelow, preferably 0.040 inches and below, more preferably 0.030 inchesand below, and most preferably 0.025 inches and below. The moldedthin-walled golf balls are preferably dipped in an isocyanate solutionfor 1 to 10 minutes (preferably 1 to 5 minutes); the isocyanate may bealiphatic or aromatic, such as HDI, IPDI, MDI, TDI type or others asdiscussed below and the isocyanate solution may range from 10 to 100%solids. The solvent used to reduce the solids and make the isocyanatesolutions may be a ketone or acetate or any solvent that will allowpenetration of the isocyanate into the cover material without distortingthe cover. After dipping, the balls are air-dried for 1 hour and thenpost-cured at 175° F. for 4 hours. After the post-cure the balls may becleaned with isopropanol to remove any excess isocyanate from the coverand the balls are then finished in a normal manner. Preferably, theisocyanate used is of the MDI type at 15-30% solids reduced with aketone (such as Mondur ML™ from Bayer Corporation) and dipped for 2-3minutes. Most preferably, the solids level is about 16 to 24% (20.+−0.4). It is beneficial that the MDI remain in a liquid state at roomtemperature. However, this method shall not be limited to the type ofpolyurethane, polyurea or polyurethane/polyurea material, isocyanateused, concentration of the isocyanate solution, solvent used, dip time,or method of application described above.

Isocyanate Indexing: In some embodiments, the cross-linking may takeplace as a result of the relative proportions of isocyanate functionalgroups in the cover layer and the coating layer. As is generally known,polyurethanes (whether thermoplastic or thermoset) are polymerizedthrough the reaction between an isocyanate functional group on apolyisocyanate and a hydroxyl functional group on a polyol. The relativestoichiometric amounts of each of these functional groups is expressedas the “isocyanate index” of the polyurethane system. Namely, theisocyanate index may be expressed as the ratio of the number ofisocyanate groups present in the polyurethane system to the number ofhydroxyl groups times 100. Or, in other words, the isocyanate index maybe expressed as the ratio of the actual number of isocyanate functionalgroups present in the polyurethane system to the hypothetical number ofisocyanate functional groups necessary to fully react with all of thehydroxyl groups present in the polyurethane system.

The isocyanate index may also be referred to as the “NCO index.” Thelocation of the decimal place may vary based on common convention (i.e.the value of the isocyanate index may be equally expressed as 1.00 or100 depending on colloquialism). As used herein, an isocyanate indexvalue of 100 means that the number of isocyanate functional groupspresent in the polyurethane system is equal to the number of hydroxylfunctional groups present in the polyurethane system. An isocyanateindex value of less than 100 means that excess hydroxyl groups arepresent, and an isocyanate index value of greater than 100 means thatexcess isocyanate groups are present.

In certain embodiments, the isocyanate index of the coating layer may bedifferent from the isocyanate index of the cover layer. Particularly,the isocyanate index of the coating layer may differ from 100 by a firstcertain amount, the isocyanate index of the cover layer may differ from100 by a second certain amount, where one of the isocyanate index valuesis above 100 and the other is below 100. More specifically, theisocyanate index of the coating layer may be at least a firstpredetermined amount above 100, while the isocyanate index of the coverlayer may be at least a second predetermined amount below 100. The firstpredetermined amount and the second predetermined amount may be the sameor different. In other embodiments, the isocyanate index of the coatinglayer may be at least a first predetermined amount below 100, while theisocyanate index of the cover layer may be at least a secondpredetermined amount above 100.

It should be understood that the different embodiments for coating thegolf balls as described above are for illustrative purposes only and notmeant to be restrictive. Other embodiments include, for example, aprocess where the molded TPU golf ball is first sprayed with apolyurethane primer further containing an excess of isocyanate(over-indexed) by at least 105 or more, and more preferably by 110 ormore. After drying (evaporation of solvent) and cure of both the PUprimer and at least a portion of the TPU outermost skin, a second stepof applying a PU topcoat is performed. A preferred means of drying andcuring in all golf ball coating embodiments is via Infrared heat.

In a second example, the molded TPU golf ball is first sprayed with apolyurethane primer further containing an excess of isocyanate(over-indexed) by at least 105 or more, and more preferably by 110 ormore. After drying (evaporation of solvent) and cure of both the PUprimer and at least a portion of the TPU outermost skin, a second stepof applying a PU topcoat which is under-indexed occurs. The polyol richPU topcoat will react with any unreacted Isocyanate leftover from theover-indexed prime-coat. The topcoat is under-indexed to 98 or less, andpreferably 95 or less.

In a third example, the molded TPU golf ball is first sprayed with asimple solution of isocyanate in a solvent. After an appropriatedrying/reacting time and temperature, a PU prime coat (which may or maynot be over-indexed) is applied followed by the application of a PUtop-coat (which may or may not be under-indexed).

In a fourth example, the molded TPU golf ball is first sprayed asdescribed above in Examples 1, 2, or 3, except that a reaction enhancingcatalyst is added to any coating. Such a catalyst promoted the reactionof isocyanate and TPU and also ensures reaction of nearly all,preferably all, of the excess isocyanate present in the golf ball coverand/or coating layers. The catalyst may comprise at least one memberselected from the group consisting of dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diazo compounds, and potassiumacetate.

Prior to the application of any coating it may be desirable to heat thegolf ball to enhance/improve the ability of the isocyanate in thecoating to react with the TPU. Infrared (IR) heat may be an ideal way toquickly warm the cover layer. A warm coating may also improve thereaction/reaction rate.

Prior to spraying the golf ball with any coating, any number ofpre-treatments may be used to effect greater/higher degree ofcross-linking between the isocyanate and TPU such as: a) spray/dippingthe TPU ball with solvent only; b) corona or plasma treatment of the TPUball; c) adding catalyst to the TPU composition; d) addingisocyanate/isocyanate masterbatch to the TPU composition; e) addingantioxidant/antiozonant, HALS, UV absorber, and the like to the TPUcomposition or any TPU coating layer; f) under-indexing the TPUcomposition to a polyol rich index to provide more sites for subsequentreaction with the isocyanate; g) adding unsaturated reactive sites tothe TPU (e.g., diene) for free-radical crosslinking that wouldultimately combine a variety of crosslinks to the TPU cover. Such meansof free radical crosslinking would be radiation (gamma, e-beam) or if aperoxide or other initiator is added to the TPU in bulk or via solutiontreatment, heat could then be used to cross-link the composition.

Treatment with Polyamines and Polyimines

In other embodiments, the golf ball having the thermoplasticpolyurethane cover is treated with multi-functional amine or iminecompounds. For example, in one embodiment, a mixture comprising: i) atleast one compound selected from the group consisting ofmulti-functional amines, imines, and isocyanates; and ii) solvent isapplied to the polyurethane outer cover. Isocyanate compounds aredescribed above. The amines contain amine groups, which are organiccompounds derived from ammonia (NH₃) by replacing one or more hydrogenatoms with alkyl or aryl groups. The imines contain imine groups, whichare nitrogen-containing organic compounds having a carbon to nitrogendouble bond, which can be represented by the general formula, R—CH═NH,where R is an alkyl or aryl group. Suitable multi-functional amine,imine, and isocyanate compounds are described further below. The mixturealso may contain additives such as, for example, ultraviolet (UV) lightstabilizers. This treatment of the outer cover layer withmulti-functional amine, imine, and isocyanate compounds further enhancescross-linking and improves cover durability. These compounds canfunction as cross-linkers in the thermoplastic polyurethane cover. Thechain length of the thermoplastic polyurethane is extended and thus themolecular weight of the polyurethane is increased when treated with themulti-functional compounds.

Next, a first (primer) polyurethane coating comprising unreactedisocyanate groups and having an isocyanate index of at least about 115is applied to the outer cover. In a third step, the golf ball ispreferably treated with heat so the coating is at least partially-cured.For example, the golf ball can be heated preferably to a surfacetemperature of at least about 105° to about 200° F. Preferably, the golfball is heated to a surface temperature of about 120° to about 150° F.Preferably, the golf ball is then heated for at a period of 2 minutes toabout 240 minutes, more preferably a period of 4 minutes to 120 minutes,and most preferably about 8 minutes to 60 minutes. In a fourth step, asecond (top-coat) polyurethane coating is applied to the outer cover.Any suitable coating technique may be used to apply the first and secondpolyurethane coatings. For example, spraying, dipping, brushing, orrolling methods can be used. Then the golf ball can go through a seriesof finishing steps.

In a second embodiment, there is a step-wise treatment of the golf ballwith first and second mixtures. The first mixture comprising: i) atleast one compound selected from the group consisting ofmulti-functional amines, imines, and isocyanates; and ii) solvent isapplied to the polyurethane outer cover. The second mixture comprising:i) at least one compound selected from the group consisting ofmulti-functional amines, imines, and isocyanates; and ii) solvent isapplied to the polyurethane outer cover. In a third step, a coatingcomprising a first (primer) polyurethane comprising unreacted isocyanategroups and having an isocyanate index of at least about 115 is appliedto the outer cover and the golf ball is treated with heat as describedabove. In a fourth step, a second (top-coat) polyurethane coating havingan isocyanate index of less than 96 is applied to the outer cover.

In a third embodiment, a first (primer) polyurethane coating comprisingunreacted isocyanate groups and unreacted amine groups is applied to theouter cover. The golf ball is treated with heat as described above. In athird step, a second (top-coat) polyurethane coating is applied to theouter cover as described above.

The thermoplastic polyurethane composition of the outer cover layer andpolyurethane coatings also may contain catalysts. Suitable catalystsinclude, for example, dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diazo compounds, and potassiumacetate, and mixtures thereof.

Suitable multi-functional amines that can be used in accordance withthis invention include diamines, such as,4,4′methylene-bis-(3-chloro-2,6-diethylaniline), available commerciallyas Lonzacure M-CEDA™. Another suitable diamine is 4,4′methylene-bis-(2,6-diethylaniline), available commercially as LonzacureM-DEA™. Both diamines have melting points at approximately 90° C. In onepreferred embodiment, the diamine is added in solid form and dry blendedwith the MDI and thermoplastic urethane base material. Alternativecross-linking agents and other solid or crystalline diamines which maybe used include: MOCA (4,4′-methylenebis-(o-chloroaniline)), MDA(methylene dianiline), as well as any other methylene bis-aniline suchas Lonzacure M-CEDA™ described above. Any other diamine-based compoundscan be made in solid crystalline form suitable for dry blending can alsobe used. The diamines above can also be added in the liquid orsemi-liquid form. Another suitable diamine is diethyl2,4-toluenediamine, which is available under the brand name, Ethacure™100, or E100, from Albermarle of Baton Rouge, La.

In an alternative embodiment, hydroquinone (HQEE) replaces the diamineconstituent and is added to the mixture of MDI and thermoplasticurethane. As described above, in one preferred embodiment, the HQEE isadded to the mixture in solid form and dry blended with the MDI andthermoplastic urethane base material. In yet another alternativeembodiment, HQEE is added in conjunction with a diamine.

In one embodiment, the multi-functional amine compound is selected fromthe group consisting of diethylene toluene diamine, mono ordi-isopropanolamine, methy diethanol amine, methylene-bis-chlorodiethylaniline, and mixtures thereof. Suitable multi-functional iminecompounds include for example, aziridines (ethyleneimines) or theirderivatives thereof. Imides and polyimides such as carbodiimides ortheir derivatives also can be used. Preferred imides are carbodiimidesand (poly)carbodiimide modified isocyanates such as Carbodiimidemodified MDI (diphenylmethane diisocynate) an example of which isSuprasec™ 9561 sold by Huntsman Polyurethanes. Another example isLupranate™ sold by BASF Polyurethanes North America, and still anotherpolycarbodiimide modified MDI is sold by Dow Plastics under thetradename, Isonate™ 143LP. Examples of the derivatives of ethyleneimineinclude 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl) propionate],diphenylmethane-bis-4,4′-N,N′-diethyleneurea. The carbodiimidederivatives are represented by the formula, R—N═C—N—R in which R, thesame or different, is alkyl or aryl. Examples of the carbodiimidoderivatives are 1-ethyl-3-(3′-dimethylaminopropyl) carbodiimide which ispreferred, dicyclohexylcarbodiimide, diphenylcarbodiimide,di-paratoluylcarbodiimide and the like.

In another embodiment, a mixture comprising: i) at least one compoundselected from the group consisting of multi-functional amines andimines; and ii) solvent is applied to the polyurethane outer cover.Next, a first (primer) polyurethane coating comprising little or noexcess isocyanate groups and having an isocyanate index of 110 or less,preferably 105 or less, and is applied to the outer cover. The index maybe about 100 or in a range of about 95 to 99. In a third step, the golfball is preferably treated with heat so the coating is at leastpartially-cured. In a fourth step, a second (top-coat) polyurethanecoating is applied to the outer cover. The top coat also contains littleto no excess isocyanate groups and has an isocyanate index of 110 orless, preferably 105 or less.

Isophorone diamine, diisopropanolamine, dimethylthiotoulenediamine, andmonomethylthiotoulenediamine, and blends thereof may also be used. Othersuitable amine and imine compounds include ethylene diamine;hexamethylene diamine; 1-methyl-2,6-cyclohexyl diamine; 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;N,N′-diisopropyl-isophorone diamine;1,4-bis-(sec-butylamino)-cyclohexane;1,2-bis-(sec-butylamino)-cyclohexane; derivatives of4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 4,4′-dicyclohexylmethanediamine; 1,4-cyclohexane-bis-(methylamine);1,3-cyclohexane-bis-(methylamine); diethylene glycolbis-(aminopropyl)ether; 2-methylpentamethylene-diamine;diaminocyclohexane; diethylene triamine; triethylene tetramine;tetraethylene pentamine; propylene diamine; 1,3-diaminopropane;dimethylamino propylamine; diethylamino propylamine;imido-bis-(propylamine); monoethanolamine, diethanolamine;triethanolamine; monoisopropanolamine, diisopropanolamine;isophoronediamine; polyoxypropylene diamine; propylene oxide-basedtriamine; 3,3′-dimethyl-4,4′-diaminocyclohexylmethane; and mixturesthereof.

These treatment mixtures can be used in the form of concentrated liquidsor semi-liquids or the solids content can be diluted by using solvents.Suitable solvents include, for example, compounds selected from thegroup consisting of alcohols such as isopropyl alcohol; aromatichydrocarbons such as toluene and xylene; esters such as ethyl acetate;water; and the like. These solvents are used to reduce the solids in themixture and make the solution. Other suitable solvents include, forexample, compounds selected from the group consisting of ketones,acetates, and mixtures thereof.

Suitable isocyanate compounds include, for example, 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluenediisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI),tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate(PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethanediisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI) andisophorone diisocyanate (IPDI); and hexamethylene diisocyanate (HDI).

As noted above, the polyurethane compositions contain urethane linkagesformed by reacting an isocyanate group (—N═C═O) with a hydroxyl group(OH). The polyurethanes are produced by the reaction of amulti-functional isocyanate (NCO—R—NCO) with a long-chain polyol havingterminal hydroxyl groups (OH—OH) in the presence of a catalyst and otheradditives. The chain length of the polyurethane prepolymer is extendedby reacting it with short-chain diols (OH—R′—OH). The resultingpolyurethane has elastomeric properties because of its “hard” and “soft”segments, which are covalently bonded together. Polyurea compositionsalso can be formed in accordance with this invention. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). The chainlength of the polyurea prepolymer is extended by reacting the prepolymerwith an amine curing agent. Hybrid poly(urethane/urea) compositionscontaining urethane and urea linkages also may be used. Any suitablepolyurethane, polyurea, and hybrids, copolymers, and blends thereof maybe used in accordance with this invention.

Thickness and Hardness of Golf Balls

The golf balls of this invention provide the ball with a variety ofadvantageous mechanical and playing performance properties as discussedfurther below. In general, the hardness, diameter, and thickness of thedifferent ball layers may vary depending upon the desired ballconstruction. If the ball includes an intermediate layer or inner coverlayer, the hardness (material) is about 50 Shore D or greater, morepreferably about 55 Shore D or greater, and most preferably about 60Shore D or greater. In one embodiment, the inner cover has a Shore Dhardness of about 62 to about 90 Shore D. In one example, the innercover has a hardness of about 68 Shore D or greater. In addition, thethickness of the inner cover layer is preferably about 0.015 inches toabout 0.100 inches, more preferably about 0.020 inches to about 0.080inches, and most preferably about 0.030 inches to about 0.050 inches.

The outer cover preferably has a thickness within a range having a lowerlimit of about 0.004 or 0.010 or 0.020 or 0.030 or 0.040 inches and anupper limit of about 0.050 or 0.055 or 0.065 or 0.070 or 0.080 inches.Preferably, the thickness of the outer cover is about 0.020 inches orless. The outer cover preferably has a surface hardness of 65 Shore D orless, or 55 Shore D or less, or 50 Shore D or less, or 50 Shore D orless, or 45 Shore D or less. Preferably, the outer cover has hardness inthe range of about 20 to about 59 Shore D. In one example, the outercover has hardness in the range of about 25 to about 55 Shore D.

The method of this invention is particularly effective in providing golfballs having a thin outer cover layer. Furthermore, the method of thisinvention provides thin outer covers with substantially uniformthickness. The resulting balls of this invention have good impactdurability and cut/shear-resistance. The United States Golf Association(“USGA”) has set total weight limits for golf balls. Particularly, theUSGA has established a maximum weight of 45.93 g (1.62 ounces) for golfballs. There is no lower weight limit. In addition, the USGA requiresthat golf balls used in competition have a diameter of at least 1.68inches. There is no upper limit so many golf balls have an overalldiameter falling within the range of about 1.68 to about 1.80 inches.The golf ball diameter is preferably about 1.68 to 1.74 inches, morepreferably about 1.68 to 1.70 inches. In accordance with the presentinvention, the weight, diameter, and thickness of the core and coverlayers may be adjusted, as needed, so the ball meets USGA specificationsof a maximum weight of 1.62 ounces and a minimum diameter of at least1.68 inches.

Preferably, the golf ball has a Coefficient of Restitution (COR) of atleast 0.750 and more preferably at least 0.800 (as measured per the testmethods below.) The core of the golf ball generally has a compression inthe range of about 30 to about 130 and more preferably in the range ofabout 70 to about 110 (as measured per the test methods below.) Theseproperties allow players to generate greater ball velocity off the teeand achieve greater distance with their drives. At the same time, therelatively thin outer cover layer means that a player will have a morecomfortable and natural feeling when striking the ball with a club. Theball is more playable and its flight path can be controlled more easily.This control allows the player to make better approach shots near thegreen. Furthermore, the outer covers of this invention have good impactdurability and mechanical strength.

Referring to FIG. 1, a front view of a finished golf ball that can bemade in accordance with this invention is generally indicated at (10).The dimples (12) may have various shapes and be arranged in variouspatterns to modify the aerodynamic properties of the ball.

As shown in FIG. 2, a two-piece golf ball (14) can be made having a core(16) and a surrounding thermoplastic polyurethane outer cover layer(18). In the golf ball (14), the core (16) has a relatively largediameter and the outer cover (18) has a relatively small thickness.Referring to FIG. 3, in another embodiment, a two-piece golf ball (20)having a smaller core (22) and a thicker outer cover layer (24) can bemade. Turning to FIG. 4, a three-piece golf ball (26) is made, whereinthe dual-layered core (inner core (28) and outer core layer (30) issurrounded by a single-layered thermoplastic polyurethane cover (32).

In FIG. 5, a partial cut-away view of a three-piece golf ball (42)having an inner core (44), outer core (46) and surrounding thermoplasticpolyurethane cover (48) is shown. Finally, in FIG. 6, a four-piece ball(50) containing a dual-core having an inner core (52) and outer corelayer (54) is shown. The dual-core is surrounded by a multi-layeredcover with an inner cover layer (56) and thermoplastic polyurethaneouter cover (60).

It should be understood that the golf balls shown in FIGS. 1-6 are forillustrative purposes only, and they are not meant to be restrictive.Other golf ball constructions can be made in accordance with thisinvention.

EXAMPLES

The following prophetic examples describe golf balls havingthermoplastic polyurethane covers that can be made in accordance withthis invention. First, polybutadiene rubber or other suitablecompositions as described above can be used to form the cores followingstandard core-prep techniques. Single or multi-layered cores can beprepared. For example, a dual-core structure having an inner core madefrom polybutadiene rubber and a surrounding outer core layer made fromethylene acid copolymer ionomer can be prepared. The cover layers areformed over the ball sub-assembly (the core structure and anyintermediate layers disposed about the core) using any suitable method.For example, the cores can be set in a mold and thermoplasticpolyurethane (TPU) compositions can be molded over the cores usingmolding techniques such as injection-molding. In a third step, the TPUcover balls can be treated, for example, by dipping in solutionscontaining epoxy-functional compounds.

Example 1

Golf balls having a thermoplastic polyurethane (TPU) cover made frompolytetramethylene glycol, 4,4′-methylenediphenyl diisocyanate and1,4-butane diol such as Texin 990 from Covestro are prepared. The moldedTPU cover golf balls are treated by one of the following methods:

Sample A—The molded TPU cover balls are dipped in a solution of 15% EPON828 (diglycidyl ether of bisphenol A resin) from Hexion in acetone for 1to 10 minutes. Then, the balls are rinsed in clean acetone before beingheated at about 160° F. for 3 to 12 hours.

Sample B—The molded TPU cover golf balls are dipped in a solution of 15%HELOXY 48 (trimethylolpropane triglycidyl ether) from Hexion in acetonefor 1 to 10 minutes. Then, the balls are rinsed in clean acetone beforebeing heated at about 160° F. for 3 to 12 hours.

It is expected the Sample A and Sample B treated golf balls will have anincrease in cover surface hardness of up to about 1 to about 5 Shore Cunits and show improvement in shear impact durability.

Example 2

Golf balls having a thermoplastic polyurethane (TPU) cover made from ablend of polytetramethylene glycol, 4,4′-methylenediphenyl diisocyanate,and 1,4-butane diol such as Texin 990 from Covestro and an ethyleneglycidylmethacrylate copolymer such as Lotader AX8840 at a ratio of90:10 are prepared. The molded TPU cover golf balls are treated by thefollowing method:

Sample A—The molded TPU cover golf balls are dipped in a 15% solution ofaminoethylpiperazine in acetone for 1 to ten minutes. Then, the ballsare rinsed in clean acetone and is heated at 160° F. for 3 to 12 hours.

It is expected the Sample A treated golf balls will have an increase incover surface hardness of up to about 1 to about 5 Shore C units andshow improvement in shear impact durability.

Example 3

Golf balls having a thermoplastic polyurethane (TPU) cover made from ablend of polytetramethylene glycol, 4,4′-methylenediphenyl diisocyanate,and 1,4-butane diol such as Texin 990 from Covestro and a polypropylenebased triamine such as Jeffamine T-403 at a ratio of 90:10 are prepared.The molded TPU cover golf balls are treated by one of the followingmethods:

Sample A—The molded TPU cover golf balls are dipped in a solution of 15%EPON 828 (diglycidyl ether of bisphenol A resin) from Hexion in acetonefor 1 to 10 minutes. Then, the balls are rinsed in clean acetone beforebeing heated at about 160° F. for 3 to 12 hours.

Sample B—The molded TPU cover golf balls are dipped in a solution of 15%HELOXY 48 (trimethylolpropane triglycidyl ether) from Hexion in acetonefor 1 to 10 minutes. Then, the balls are rinsed in clean acetone beforebeing heated at about 160° F. for 3 to 12 hours.

It is expected the Sample A and Sample B treated golf balls will have anincrease in cover surface hardness of up to about 1 to about 5 Shore Cunits and show improvement in shear impact durability.

Test Methods

Hardness. The center hardness of a core is obtained according to thefollowing procedure. The core is gently pressed into a hemisphericalholder having an internal diameter approximately slightly smaller thanthe diameter of the core, such that the core is held in place in thehemispherical portion of the holder while concurrently leaving thegeometric central plane of the core exposed. The core is secured in theholder by friction, such that it will not move during the cutting andgrinding steps, but the friction is not so excessive that distortion ofthe natural shape of the core would result. The core is secured suchthat the parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dor Shore A hardness) was measured according to the test method ASTMD-2240.

Compression. As disclosed in Jeff Dalton's Compression by Any OtherName, Science and Golf IV, Proceedings of the World Scientific Congressof Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”), severaldifferent methods can be used to measure compression, including Atticompression, Riehle compression, load/deflection measurements at avariety of fixed loads and offsets, and effective modulus. For purposesof the present invention, compression refers to Soft Center DeflectionIndex (“SCDI”). The SCDI is a program change for the Dynamic CompressionMachine (“DCM”) that allows determination of the pounds required todeflect a core 10% of its diameter. The DCM is an apparatus that appliesa load to a core or ball and measures the number of inches the core orball is deflected at measured loads. A crude load/deflection curve isgenerated that is fit to the Atti compression scale that results in anumber being generated that represents an Atti compression. The DCM doesthis via a load cell attached to the bottom of a hydraulic cylinder thatis triggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Coefficient of Restitution (“COR”). The COR is determined according to aknown procedure, wherein a golf ball or golf ball sub-assembly (forexample, a golf ball core) is fired from an air cannon at two givenvelocities and a velocity of 125 ft/s is used for the calculations.Ballistic light screens are located between the air cannon and steelplate at a fixed distance to measure ball velocity. As the ball travelstoward the steel plate, it activates each light screen and the ball'stime period at each light screen is measured. This provides an incomingtransit time period which is inversely proportional to the ball'sincoming velocity. The ball makes impact with the steel plate andrebounds so it passes again through the light screens. As the reboundingball activates each light screen, the ball's time period at each screenis measured. This provides an outgoing transit time period which isinversely proportional to the ball's outgoing velocity. The COR is thencalculated as the ratio of the ball's outgoing transit time period tothe ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

It is understood that the manufacturing methods, compositions,constructions, and products described and illustrated herein representonly some embodiments of the invention. It is appreciated by thoseskilled in the art that various changes and additions can be made tocompositions, constructions, and products without departing from thespirit and scope of this invention. It is intended that all suchembodiments be covered by the appended claims.

What is claimed is:
 1. A golf ball formed by a method, the methodcomprising the steps of: providing a golf ball sub-assembly comprisingat least one core layer; forming an outer cover layer over thesub-assembly, wherein the outer cover layer is formed from a firstcomposition comprising a thermoplastic polyurethane and epoxy-functionalcompound; and applying a second composition comprising an epoxy curingagent to the outer cover layer to form at least a partially cross-linkedcover for the golf ball.
 2. The golf ball of claim 1, wherein the firstcomposition further comprises a catalyst.
 3. The golf ball of claim 2,wherein the catalyst is selected from the group consisting of dibutyltin dilaurate, dibutyl tin acetylacetonate, dibutyl tin dibutoxide,dibutyl tin sulfide, dibutyl tin di-2-ethylhexanoate, dibutyl tin (IV)diacetate, dialkyltin (IV) oxide, tributyl tin laurylmercaptate, dibutyltin dichloride, organo lead, tetrabutyl titanate, tertiary amines,mercaptides, stannous octoate, potassium octoate, zinc octoate, diaz0compounds, and potassium acetate, and mixtures thereof.